In the past, internal gears and splines have been predominantly manufactured with two cutting methods: broaching and shaping.
Broaching involves the use of a broach, an elongated cutting tool having a series of cutting surfaces of increasing size. The broach is passed through the gear bore with the first cutting surface engaging the bore of the blank and thereby removing a small amount of material. With the passage of each successive cutting surface, with their increasing sizes, the length of the gear or spline teeth being made increases. Typically, when the broach passes completely through the bore, the gear or spline has been cut.
Shaping is a process which involves using a shaper-cutter tool which resembles, in appearance, a gear and a machine to manipulate this shaper-cutter tool. Shaping uses a reciprocating motion to cut. For every stroke of a cutter ram, the shaper-cutter tool travels through the bore, taking a slight cut. It then retracts from the edge of the bore and returns to the top of the stroke cycle and repositions itself for the next cutting stroke. This process is repeated until the desired tooth size is reached.
While both broaching and shaping have been successfully used to cut internal gears and splines in the past, they each have drawbacks. Broaches are typically quite expensive. They are often custom built to meet the peculiar needs of a particular gear- and spline-cutting job. They require frequent sharpening and have a limited useful life. Shaping cutters also require frequent sharpening and are relatively slow cutting, owing to the fact that they cut only during portions of one stroke. Because of this, they are actually cutting less than 50 percent of the time they are in operation.
Consequently, there exists a need for improved methods and apparatuses for manufacturing internal gears and splines.